Orientadores: Ana Rita Morales, Leila Peres / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T15:46:33Z (GMT). No. of bitstreams: 1 Cruz_CarolinaVertuMarinhoda_M.pdf: 4798053 bytes, checksum: 65af0005636fd070fa8ddccf682f09f9 (MD5) Previous issue date: 2013 / Resumo: O trabalho teve como objetivo estudar o desempenho de filmes flexíveis de nanocompósitos visando aplicação na área de embalagens. Partindo-se de uma blenda típica do mercado, de polietileno de alta densidade - PEAD, com polietileno de baixa densidade linear - PEBDL, foram preparados nanocompósitos com uma argila montmorilonita organofílica comercial. Na primeira parte experimental foi elaborado, em uma extrusora de dupla rosca, um concentrado ou masterbatch de argila montmorilonita com resina compatibilizante à base de polietileno de baixa densidade linear enxertado com anidrido maléico - PEBDL-AM e partir deste concentrado foram feitos filmes com uma blenda de PEAD e PEBDL com o objetivo de se obter uma estrutura esfoliada da argila na matriz polimérica. A morfologia do concentrado e dos filmes de nanocompósitos foi caracterizada por Difração de Raios-X e Microscopia Eletrônica de Varredura - MET, bem como foram avaliadas as propriedades de barreira ao gás oxigênio e vapor d'água e as propriedades mecânicas dos filmes produzidos. A partir da análise dos resultados da primeira parte experimental, executou-se a segunda parte experimental, onde se mudaram as condições de processamento e a formulação do masterbatch visando uma melhor dispersão da nanocarga. Novos filmes foram preparados como o masterbatch e a blenda de PEAD e PEBDL e as mesmas propriedades da parte experimental I foram estudadas. As variáveis de processamento do masterbatch e o teor de argila influenciaram a dispersão da argila e os resultados de permeabilidade dos filmes obtidos. O modelo de Nielsen foi aplicado para estimar a razão de aspecto e para entender o grau de esfoliação da argila. Melhorias nas propriedades de barreira foram observadas, o que indica que os sistemas estudados mostram-se promissores para aplicações em embalagens flexíveis / Abstract: The objective of this work was to study the properties of a flexible film based in nanocomposites for packaging application. Assuming a typical blend of HDPE and LLDPE, nanocomposites were prepared with commercial organophilic clay. In the first experimental part, a masterbatch was prepared from a linear low density polyethylene modified with maleic anhydride and a montmorillonite clay. The masterbatch was diluted in a blend of high density polyethylene (HDPE) with linear low density polyethylene (LLDPE) and films were extruded. The objective was to obtain nanocomposites whitin an exfoliated structure of the clay in the polymer matrix. The nanocomposites morphologies were evaluated by X-ray diffraction and TEM. Besides, the properties of gas barrier to oxygen and water vapor and mechanical properties were also determined. Analyzing the results of the first experimental part, improvement on the clay dispersion based on the processing conditions was expected and the second experimental part was held. The conditions of processing and masterbatch formulation were changed. Dilutions were also made in the blend of HDPE / LLDPE for films preparation and the same properties of the experimental I were studied. Processing conditions and clay content affect the ability of the clay dispersion and the results of permeability. Nielsen's model was applied in order to measure the aspect ratio and to understand the clay exfoliation level. Improvements on the barrier properties were observed and the studied systems were shown to be promising for applications in flexible packaging / Mestrado / Ciencia e Tecnologia de Materiais / Mestra em Engenharia Química

Orientador: Fernando Galembeck / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-14T14:09:30Z (GMT). No. of bitstreams: 1 Linares_ElisangelaMoura_M.pdf: 5164980 bytes, checksum: d9e4505544f0a48a985e78fccc9e1832 (MD5) Previous issue date: 2009 / Resumo: Este trabalho mostra o efeito da distribuição de espécies iônicas na morfologia e nas propriedades mecânicas de filmes de blendas de látices, e também demonstra o uso da técnica de microscopia eletrônica de transmissão por energia filtrada (EFTEM) para caracterização morfológica das blendas e de seus nanocompósitos com argila, explorando a região de baixa perda de energia de elétrons. Blendas de látex de borracha natural (NR)/poli(estireno-acrilato de butila) [P(S-BA] e NR/poli(cloreto de vinila) [PVC] foram investigadas, utilizando-se microscopia de varredura de potencial elétrico (SEPM). Através dos mapas de potencial elétrico, foi verificada a ocorrência de migração de espécies iônicas da blenda de uma fase polimérica para a outra, durante a preparação da blenda. Esta migração é espontânea, porque permite a redução da energia do sistema através da diminuição da repulsão eletrostática entre íons, distribuindo-os entre as fases, e é direcionada para o polímero que inicialmente tem menor concentração de cargas e apresenta maior constante dielétrica. Os domínios formados pelos dois componentes da blenda apresentam sinais de carga opostos, o que contribui para o aumento na compatibilidade, através da adesão eletrostática. Os espectros de baixa perda de energia mostram diferenças nas estruturas moleculares dos polímeros das blendas. Essas diferenças se expressam através de mudanças de contraste em imagens de perda de energia (mapas moleculares) adquiridas entre 20 e 90 eV. Blendas de NR/P(S-BA), P(S-BA)/PVC, P(S-BA)/poli(estirenometacrilato de 2-hidroxietila) e seus respectivos nanocompósitos foram analisados por EFTEM que revelou domínios em escala nanométrica, mesmo tendo pequenas diferenças na composição química, sem a necessidade de corar a amostra. Nos nanocompósitos, a disposição das lamelas de argila foi revelada graças ao cancelamento do contraste entre os polímeros. / Abstract: This work shows the effect of ionic specie distribution on the morphology and on the mechanical properties of latex blend films, as well as it demonstrates the use of energy-filtered transmission electron microscopy (EFTEM) technique to morphological characterization of these blends and its clay nanocomposites, by exploring the low-loss electron energy region. Natural rubber (NR)/poly(styrenebutyl acrylate) [P(S-BA)] and NR/poly(vinyl chloride) [PVC] blends were investigated by scanning electric potential microscopy (SEPM). Using the electric potential maps, it has been observed ionic specie migration from one polymer phase towards the other, during blend preparation. The migration is spontaneous because it allows the reduction of system energy thanks to the decreasing of ionion electrostatic repulsion given by ion distribution throughout the phases. The migration is directed towards the polymer that has initially the lower charge concentration and that presents the higher dielectric constant. The domains formed by the two blend component present opposite charge signals, which contribute to compatibility enhancement through electrostatic adhesion. Low-energy-loss electron spectra show differences on molecular structure of polymers that form the blends. Such differences are expressed through contrast changing in low-energyloss images (molecular maps) acquired between 20 and 90 eV. NR/P(S-BA), P(SBA)/ PVC, P(S-BA)/poly(styrene-2-hydroxyethyl metacrylate) and their respective clay nanocomposites have been analyzed by EFTEM without staining and it revealed nano-sized domains, even when chemical composition was slightly different. Clay platelet distribution within nanocomposites was revealed due to contrast canceling of polymer domains on EFTEM images. / Mestrado / Físico-Química / Mestre em Química

No description available.

Orientador: João Sinézio de Carvalho Campos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-27T19:06:13Z (GMT). No. of bitstreams: 1 Conceicao_RafaelNovaesda_M.pdf: 10111957 bytes, checksum: 9168b5514bd29d6ead99888af5052aab (MD5) Previous issue date: 2015 / Resumo: É bem conhecida a necessidade de energia elétrica para o bem estar e desenvolvimento tecnológico da população em nosso planeta. Ao lado dos avanços científicos de novas tecnologias para geração, existem interesses na melhoria do transporte da energia. Dentre estes se encontram materiais para isolação elétrica de barras estatóricas, quer sejam para melhorar a isolação ou mesmo para reduzir custos. Assim, o presente trabalho visa apresentar resultados da aplicação de uma nova resina epóxi bisfenólica (DGEBF) (RN) à base de nanopartículas de sílica e comparar suas propriedades com a resina epóxi bisfenólica (DGEBA) (RE), atualmente utilizada para a isolação de hidrogeradores. Neste sentido, fabricaram-se protótipos de barras estatóricas, destinadas a hidrogeradores, sendo as resinas impregnadas em sistema VPI (Vácuo-Pressão-Impregnação) e avaliaram-se as propriedades físico-químicas pelas técnicas de viscosimetria, TGA, DSC, MEV e EDS. As propriedades elétricas foram avaliadas pelas técnicas de fator de dissipação (tan delta), descargas parciais, envelhecimento acelerado (VET) e tensão de ruptura. Dentre os resultados das propriedades físico-químicas pode-se comprovar um aumento inicial de três vezes o valor de viscosidade para resina RN em comparação com RE. Entretanto, não houve detrimento das características dielétricas em função da viscosidade, o que foi comprovado através dos resultados de tan delta e VET. Obteve-se um valor de Tg de 116°C e 145°C para RN e RE, respectivamente, o que limitaria a aplicação da resina em geradores por estar abaixo da temperatura de operação. Dentre os resultados dos testes elétricos para as resinas observou-se que: (i) o fator de dissipação e de envelhecimento são praticamente os mesmos para ambas as resinas; (ii) o valor de tip-up resultaram em 0,014 % para RE e 0,020 % para a resina RN, sendo que a norma EN 50209 exige que seja inferior a 0,25% e (iii) a estimativa do tempo de vida útil obtida foi de cerca de 40 anos para os dois tipos de resina, o que é aplicável para maioria dos enrolamentos em operação. Neste sentido sugere-se que a resina RN pode ser uma boa alternativa a resina RE, com um desempenho elétrico equivalente, desde que ajustadas suas condições de processamento e temperatura de aplicação / Abstract: It is well know the demand of electrical energy for the wellbeing and technological development of the population in our planet. Among the scientific development of new technologies for generation, are interests to optimize the energy transport. Among them are materials for electrical insulation of stator bars, whether for improving the insulation or even to reduce the costs. Therefore, the present work aim to present the results of the employment of a new bisphenolic epoxy resin (DGEBF) (RN) containing silica nanoparticles and compare its properties with the bisphenolic epoxy resin (DGEBA) (RE) currently used for the insulation of hydrogenerators. In this context, it was manufactured prototype stator bars, designed for hydrogenerators, being the resins impregnated through VPI (Vacuum-Pressure-Impregnation) system and their physicochemical properties evaluated with the technics of viscosimetry, TGA, DSC, MEV and EDS. The electrical properties were evaluated with the tests of dissipation factor (tan delta), partial discharges, voltage endurance test (VET) and breakdown. Among the results of the physicochemical properties it was possible to verify an initial increase of three times the value of viscosity for RN resin compared to RE. However there was no detriment of the dielectric characteristics depending on the viscosity, what was proven with the results of dissipation factor and VET. It was obtained a value of Tg of 116°C and 145°C for RN and RE respectively, what could limit its employment for hydrogenerators as being below the operational temperature. Among the results of electrical tests for the resins it was observed that: (i) the dissipation factor and VET are practically the same for both resins; (ii) the tip-up value resulted in 0,014% for RE and 0,020% for RN, being required lower than 0,25% according to the norm EN 50209 and (iii) the estimating lifecycle was approximately 40 years for both types of resin, what is applicable for most windings under operation. In this context it is suggested that the RN resin can be a good alternative for RE resin with an equivalent performance once the process conditions and employment temperature are adjusted / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

Submitted by Fernanda Rodrigues de Lima (fernanda.rlima@ufpe.br) on 2018-10-08T21:28:27Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) DISSERTAÇÃO Macário Granja Gonçalves.pdf: 12281899 bytes, checksum: d3655d47934222f30676882c61c7544a (MD5) / Approved for entry into archive by Alice Araujo (alice.caraujo@ufpe.br) on 2018-11-22T17:28:36Z (GMT) No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) DISSERTAÇÃO Macário Granja Gonçalves.pdf: 12281899 bytes, checksum: d3655d47934222f30676882c61c7544a (MD5) / Made available in DSpace on 2018-11-22T17:28:36Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) DISSERTAÇÃO Macário Granja Gonçalves.pdf: 12281899 bytes, checksum: d3655d47934222f30676882c61c7544a (MD5) Previous issue date: 2015-03-19 / CNPq / A utilização de semicondutores orgânicos como materiais ativos em dispositivos optoeletrônicos é uma área de intensa pesquisa e inovação nos dias de hoje. Células solares baseadas em blendas de polímeros condutores ganharam muita atenção devido a suas características mecânicas e bom rendimento, ao que se combina um baixo custo de fabricação. Neste trabalho, investigamos a influência de aspectos óticos e estruturais dos materiais utilizados sobre o transporte eletrônico em dispositivos fotovoltaicos moleculares à base de polihexiltiofeno (P3HT) e 5-(2-etil-hehilóxi)-1,4-fenileno vinileno (MEHPPV) associados com fulerenos funcionalizados (PCBO), e de nanopartículas de ouro recobertas com polianilina (PANI-AuNPs). Os filmes de P3HT e MEH:PPV foram depositados a partir das soluções coloidais por meio da técnica de spin-coating, sendo cada um dos polímeros solubilizado em clorobenzeno. Através de medidas de corrente-tensão realizadas sob luz "solar simulada", e tendo a temperatura, a tensão aplicada e a área ativa dos dispositivos como parâmetros de controle, estimamos a eficiência de conversão de energia. Vale ressaltar que normalmente as técnicas convencionais utilizadas para medir mobilidade elétrica se utilizam de arranjos elétricos e ópticos acoplados, como é o caso das medidas de Tempo de Voo (TOF). Neste trabalho, como método alternativo, nos baseamos em medidas de espectroscopia de impedância elétrica na ausência de luz e com varredura na frequência para estimar a mobilidade dos portadores de carga negativos no interior dos dispositivos. Além disso, avaliamos o efeito de fatores da preparação (velocidade de rotação, temperatura de annealing e concentração de PANI-AuNPs) dos diferentes dispositivos fotovoltaicos sobre a eficiência e a mobilidade eletrônica, de modo a estabelecer a dinâmica de condução nas diferentes células solares orgânicas nanoestruturadas investigadas. / The use of organic semiconductors as active materials in optoelectronic devices is nowadays an area of intense research and innovation. Solar cells based on blends of conductive polymers have deserved a lot of attention due to their mechanical characteristics and good efficiency, which could be attained with low manufacturing costs. In this study, we investigated the influence of optical and structural aspects of the material used for the electron transport in molecular-based photovoltaic devices polihe-xiltiofeno (P3HT) and 5-(2-ethylhehiloxi)-1,4-phenylene vinylene (MEH-PPV) associated with functionalized fullerenes (PCBO) and gold nanoparticles coated with polyaniline (PANI-AuNPs). The P3HT films and MEH:PPV were deposited from colloidal solutions through the spin-coating technique, where in each case the corresponding polymer was previously solubilized in chlorobenzene. Through current-voltage measurements performed under "simulated sunlight", and taking the temperature, the applied voltage and the active area of the devices as control parameters, we were able to estimate the corresponding energy conversion efficiency. It is noteworthy that usually the conventional techniques used to measure electric mobility involve the use of coupled electrical and optical arrangements, such as is the case of the flight time (TOF) method. In this work, based on electrical impedance spectroscopic methods, in the absence of both incident light and scanning frequency, we were able to estimate the mobility of negative charge carriers within the device. Furthermore, we evaluated the effect of the preparation factors (rotation speed, temperature and annealing concentration of PANI-AuNPs) of different photovoltaic devices on the efficiency and electron mobility in order to establish different driving dynamics in organic solar cells nanostructured investigated.

Orientador: Sidney Jose Lima Ribeiro / Coorientador: Hernane da Silva Barud / Banca: Patrícia Bento da Silva / Banca: Rosana Maria Nascimento de Assunção / Resumo: A celulose bacteriana (CB) é um nanomaterial que pode ser obtido a partir de bactérias do gênero Gluconacetobacter. O material é formado por uma rede de fios nanométricos que lhe confere enorme área superficial, surpreendente capacidade de absorção e retenção de água, boa elasticidade e fácil moldabilidade. O material também é biodegradável, biocompatível, atóxico e não alergênico. A CB pode ser sintetizada a partir de uma variedade de fontes de carbono, através de bactérias que são capazes de converter glicose à celulose como parte de seu metabolismo. Assim, a glicose atua não somente como fonte de energia para o microrganismo, mas também como precursora da biossíntese de CB. A CB produzida na superfície do meio de cultura pela bactéria Gluconacetobacter xylinus foi utilizada para a produção in situ de nanocompósitos com propriedades químicas e físicas modificadas devido a presença de laponita (LPN) que possui composição bem definida e livre de impurezas insolúveis, como partículas de sílica e óxidos de ferro. As dimensões nanométricas dessas argilas, aliadas ao seu formato circular e capacidade de produzir materiais transparentes, como filmes e dispersões, auxiliam na obtenção de nanocompósitos de alta homogeneidade. Neste trabalho foi realizada a preparação e caracterização de nanocompósitos de CB, por meio da incorporação "in situ" de LPN. Os filmes CB/LPN foram caracterizados morfologicamente, por microscopia eletrônica de varredura com EDS e microscopia de força atômica... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Bacterial cellulose (CB) is a nanomaterial that can be obtained from bacteria of the genus Gluconacetobacter. The material is formed by a network of nanometric wires that gives it enormous surface area, surprising capacity of water abs orption and retention, good elasticity and easy moldability. The material is also biodegradable, biocompatible, non - toxic and non - allergenic. CB can be synthesized from a variety of carbon sources, through bacteria that are able to convert glucose to cellu lose as part of their metabolism. Thus, glucose acts not only as a source of energy for the microorganism, but also as a precursor of CB biosynthesis. The CB produced on the surface of the culture medium trough the bacterium Gluconacetobacter xylinus was u sed for the in situ production of nanocomposites with chemical and physical properties m odified due to the presence of l aponite (LPN) that has a well defined composition and free of insoluble impurities, as particles of silica and iron oxides. The nanometr ic dimensions of these clays, combined with their circular shape and the ability to produce transparent materials, such as films and dispersions, help to obtain nanocomposites of high homogeneity. In this work the preparation and characterization of CB nan ocomposites was carried out by the in situ incorporation of LPN. The CB/LPN films were characterized morphologically by scanning electron microscopy with EDS and atomic force microscopy. Structurally, by X - ray diffraction, t he... (Complete abstract click electronic access below) / Mestre

Orientador: Lizandra Maria Zimmermann. / Dissertação (Mestrado em Química) - Programa de Pós-Graduação em Química, Centro de Ciências Exatas e Naturais, Universidade Regional de Blumenau, Blumenau.

Orientador: Michelle Leali Costa / Coorientador: Edson Cocchieri Botelho / Coorientador: Bruno Ribeiro / Banca: Luis Rogério de Oliveira Hein / Banca: Antonio Carlos Ancelotti Junior / Resumo: Os avanços tecnológicos na área dos compósitos poliméricos criaram novas oportunidades para estruturas de alto desempenho e com baixo peso, favorecendo o desenvolvimento de sistemas estratégicos em diversos setores, principalmente o aeronáutico. Dentro deste contexto os compósitos poliméricos nanoestruturados encontram-se em uma posição vantajosa em relação a outros materiais, pois seus constituintes podem agregar melhorias nos desempenhos mecânico, térmico e elétrico. Neste trabalho, compósitos nanoestruturados de poli(éter-imida) e nanotubos de carbono de paredes múltiplas (PEI/MWCNT) foram obtidos a partir da técnica de mistura em solução. Posteriormente, foi realizada a consolidação do compósito nanoestruturado reforçado com fibra de carbono (PEI/MWCNT/FC) via moldagem por compressão a quente. A partir das análises térmicas de termogravimetria (TGA) e dinâmico-mecânica (DMA) realizadas no compósito PEI/MWCNT, verificou-se uma melhoria na resistência térmica e nas propriedades viscoelásticas do material. Além disso, as melhorias nas propriedades físicas ocasionadas pela adição de MWCNT a matriz polimérica, influenciaram positivamente na qualidade de processamento dos laminados. Após os ensaios de ILSS e CST observou-se que a adição do nanoreforço gerou um incremento de 16% e 58%, respectivamente, sugerindo uma melhoria na adesão interfacial do compósito. O comportamento em tração não sofreu influência significativa a partir da adição de MWCNT, levando apenas uma melhoria d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Technological advances in polymer composites area have been created new opportunities for high-performance and lightweight structures, promoting the development of strategic systems in several sectors of industry, especially on the aerospace field. In this context, the nanostructured polymer composites are in an advantageous position compared to other materials, since its constituents may add improvements in mechanical, thermal and electrical performance. In this work, PEI/MWCNT nanostructured composites were obtained from solution mixing technique. Subsequently, the consolidation of the composite reinforced with carbon fiber, was performed by hot compression molding. TGA and DMA analyzes performed on PEI/MWCNT composite film revealed that there was an improvement in the thermal resistance and the viscoelastic properties of the material. In addition, the enhancement in physical properties due to the incorporation of MWCNT in polymer matrix had a positive role in the quality of the laminates. After ILSS and CST tests, it was observed that the addition of the nanofiller led to an increment of 16% and 58%, respectively, suggesting an improvement in the interfacial adhesion of the composite. The tensile behavior did not present a significant influence from the addition of MWCNT, leading to only a 5% improvement in tensile strength and 2% in the modulus of elasticity of the material. The addition of MWCNT did not significantly influence the fatigue strength of the laminates when a... (Complete abstract click electronic access below) / Mestre

Orientador: Lauro Tatsuo Kubota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-09-11T21:18:50Z (GMT). No. of bitstreams: 1 Silva_CeciliadeCarvalhoCastroe_M.pdf: 2199742 bytes, checksum: e0c39714ed0a9045beffe47b579b8438 (MD5) Previous issue date: 2011 / Resumo: Este trabalho descreve o desenvolvimento de um sensor amperométrico para detecção eletrocatalítica de cisteína, através da construção de uma plataforma funcional para a complexação de íons cobre. O material base desta plataforma foi um nanocompósito obtido por meio da modificação de nanotubos de carbono de paredes múltiplas (MWCNTs) com poli(4-vinilpiridina) PVP, através uma reação de polimerização in situ. Foi realizada uma otimização multivariada, empregando um planejamento composto central de face centrada, para a modificação da superfície do eletrodo de carbono vítreo (ECV), sendo a condição ótima obtida quando se utiliza concentração da dispersão de nanocompósito de MWCNTs-PVP de 6,00 mg L, concentração da solução CuCl2 de 50 mmol L e tempo de complexação dos íons cobre de aproximadamente 83 minutos. A plataforma foi caracterizada por microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva de raios-X (EDX), espectroscopia de impedância de eletroquímica (EIE), cronoamperometria e voltametria cíclica. Os valores da constante heterogênea de transferência de elétrons (ks) e da constante cinética da reação entre os íons Cu- cisteína (kobs) foram 5,78 s e 6,96 x 10 L mol s respectivamente. A curva analítica apresentou uma faixa linear de 5 a 60 mmol L para a detecção de cisteína. Já os limites de detecção e quantificação foram 1,50 e 5,00 mmol L, respectivamente. Além disso, o ECV/MWCNTs-PVP/Cu apresentou um tempo de resposta extremamente baixo, 0,10 s e quando aplicado para determinação de cisteína em amostras de suplemento alimentar apresentou resultados estatisticamente iguais em um nível de confiança de 95% com os resultados obtidos pelo método oficial / Abstract: This work describes the fabrication of an amperometric sensor for electrocatalytical detection of cysteine. The developed sensor is based on a functional platform for complexing copper ions on multi-walled carbon nanotubes (MWCNTs) modified with poly-4-vinylpyridine through an in situ reaction of polymerization. A multivariate analysis using a central composite design to investigate the surface modification of glassy carbon electrode (GCE) was employed to optimize the experimental variables. The established optimal conditions for the concentration of MWCNTs-PVP dispersed nanocomposite were, 6,00 mg L, 50 mmol L of concentration CuCl2 and around 83 min. for complexation of copper ions. The platform was characterized performing scanning electron microscopy (SEM), energy dispersive x-ray (EDX), electrochemical impedance spectroscopy (EIS), chronoamperometry and cyclic voltammetry analyses. The obtained values for the kinetic constants for heterogeneous electron transfer rate (ks) and for chemical reaction (kobs) between Cu and cysteine were 5.78 s and 6.96 L mol s, respectively. The analytical curve showed a linear range for detecting cysteine in concentrations from 5 to 60 mmol L. The detection and quantification limits obtained were 1.50 and 5.00 mmol L, respectively. Moreover, the response time of the ECV/MWCNTs-PVP/Cu sensor was 0.1 s. The application of the sensor to detect cysteine in nutritional supplement showed results statistically equal (0.95 confidence level) to those obtained with official methods / Mestrado / Quimica Analitica / Mestre em Química

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Tese (Doutorado) / Abstract: Since this thesis presents two independent studies on cellulose nanocrystals (CNCs), the abstract was divided in two sections referring to chapters II and III, respectively. Comprehensive morphological and structural investigation of cellulose I and II nanocrystals prepared by sulfuric acid hydrolysis Cellulose has several polymorphs. These polymorphs differ by crystal packing (i.e. unit cell parameters), polarity of the constituting chains and hydrogen bond patterns established between them. Most of cellulose polymorphs result from chemical treatments of the native polymorph, the so-called cellulose I (Cel-I) (Wada et al., 2008). In Cel-I, the chains are parallel and can be packed into two allomorphs, namely Iα and Iβ. Among the cellulose polymorphs, cellulose II (Cel-II), in which the chains are antiparallel, can be prepared from Cel-I by two distinct processes: Mercerization or Regeneration. Mercerization is an essentially solid-state process during which cellulose fibers are swollen in concentrated alkali media and recrystallized into cellulose II upon washing and drying (removal of the swelling agent). Unlike the mercerization process, in process known as regeneration, cellulose is first dissolved in an appropriated solvent and subsequent reprecipitated by adding a non-solvent, leading the chains to recrystallize into into Cel-II polymorph. The Cel-I to Cel-II transition is irreversible, which suggests that Cel-II is thermodynamically more stable (Habibi et al., 2010). Cell-II is the second most extensively studied polymorph due to its technical relevance. Nevertheless, so far, most of investigations involving Cel-II have focused on fibers and only a few recent studies have been carried out on CNCs. Cel-II nanocrystals have been prepared either by acid hydrolysis of mercerized fibers (Hirota et al., 2012; Kim et al., 2006; Yue et al., 2012), mercerization of Cel-I CNCs (Jin et al., 2016), or after recrystallization of fractions of short cellulose chains in solution (Dhar et al., 2015; Hirota et al., 2012; Hu et al., 2014; Sèbe et al., 2012). However, while these studies have generally combined the data from several imaging, diffraction and spectroscopic techniques, a complete structural picture of the nanocrystals has not been reported so far. In this context, the purpose of the research work presented in chapter II was to produce, characterize and compare CNCs obtained from eucalyptus wood pulp using three different methods: i) classical sulfuric acid hydrolysis (CN-I), ii) acid hydrolysis of cellulose previously mercerized by alkaline treatment (MCN-II), and iii) solubilization of cellulose in sulfuric acid and subsequent recrystallization in water (RCN-II). The morphology, crystal structure, crystallinity index, surface charge and degree of polymerization of these nanocrystals were characterized by complementary techniques, namely elemental analysis, zetametry, viscometry, transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier-transform infrared and solid-state nuclear magnetic resonance spectroscopies (FTIR and NMR, respectively). The three types of prepared CNC exhibit different morphologies and crystalline structures. When the acid hydrolysis conditions are set-up in such a way that the crystalline domains in the initial wood pulp and mercerized cellulose (WP and MWP, respectively) are preserved (60 wt% H2SO4, 45°C, 50 min), the resulting nanocrystals retain the fibrillar nature of the parent fibers (i.e., the chain axis is parallel to the long axis of the acicular particles) and their initial allomorphic type (I for WP and II for the MWP). In both cases, the particles are mostly composed of a few laterally-bound elementary crystallites, in agreement with what was shown for cotton CNCs by Elazzouzi-Hafraoui et al. (2008). The unit nanocrystals in CNCs from mercerized cellulose (MCN-II) are shorter but broader than those prepared from cellulose I fibers (CN-I). If harsher conditions are used (64 wt% H2SO4, 40°C, 20 min), resulting in the depolymerisation and dissolution of native cellulose, the short chains (with degree of polymerization DP ≈ 17) recrystallize into Cel-II ribbons upon regeneration in water at room temperature. In these somewhat tortuous ribbons, the chain axis would lie perpendicular to the long axis of the nanocrystal and parallel to its basal plane. In addition, these nanoribbons are very similar in shape and molecular orientation to mannan II nanocrystals prepared by recrystallization of mannan (Heux et al., 2005), a linear polymer of β-(1,4)-D-mannosyl residues, suggesting that this mode of crystallization may be a feature of short-chain linear β-(1,4)-linked polysaccharides. Although similar ribbons of recrystallized cellulose II have been reported by other authors, to our knowledge, it is the first time that a detailed morphological and structural description is proposed in terms of particle morphology, crystal structure and chain orientation. By comparison with the fibrillar nanocrystals prepared by acid hydrolysis of native or mercerized cellulose fibers, the unique molecular and crystal structure of the nanoribbons imply that a higher number of reducing chain ends are located at the particle surface, which may be important for subsequent chemical modification and specific potential applications such as biosensing and bioimaging agents. Therefore this study offers scope to a better understanding of crystalline structure and morphology of CNC obtained by regeneration process with sulfuric acid. Mechanical properties of natural rubber nanocomposites reinforced with high aspect ratio cellulose nanocrystals isolated from soy hulls At present, the most promising application of CNCs is as reinforcement material in the field of polymer nanocomposites.The incorporation of CNCs in polymer matrices generally leads to polymer-based nanocomposite materials with higher mechanical and barrier properties than the neat polymer or conventional composites. Among various factors that influence the efficiency of the reinforcing effect of CNCs, their intrinsic characteristics, including crystallinity and aspect ratio, play a key role (Dufresne, 2012; Favier et al., 1995; Mariano et al., 2014). It is also well-known that these characteristics depend on the source of the original cellulose, on the extraction method and its conditions (including pretreatment). However, it is widely accepted that the raw starting material is the most important factor (Beck-Candanedo et al., 2005; Dufresne, 2012; Elazzouzi- Hafraoui et al., 2008). The reinforcement capability of CNCs is therefore directly linked to the source of cellulose as well as its biosynthesis. Thus, the optimization of the extraction procedure and further characterization of CNCs from different sources of cellulose are crucial for an efficient exploitation of these sources, allowing the selection of the appropriate source (i.e. with targeted morphology) to suit specific end user applications (Brinchi et al., 2013). Natural rubber (NR) is a perfect polymer matrix to be used as a model system to study the effect of filler reinforcement, owing to its high flexibility and low stiffness. Its properties can be tailored by the addition of reinforcing fillers of various surface chemistries and aggregate size/aspect ratios to suit the targeted application. CNCs extracted from different sources have already been studied as nanoreinforcement in NRbased nanocomposites, including CNCs isolated from capim dourado (Siqueira et al., 2010), rachis of palm date tree (Bendahou et al., 2009), sugarcane bagasse (Pasquini et al., 2010; Bras et al., 2010), sisal (Siqueira et al., 2011), and bamboo (Visakh et al., 2012). So far, little results have been reported in the literature on the isolation of CNCs from soy hulls or their use in nanocomposites (Flauzino Neto et al., 2013, Silvério et al., 2014). In this study, CNCs were isolated from soy hulls by sulfuric acid hydrolysis treatment. The resulting CNCs, referred to as CNCSH in the following, were characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), wide-angle X-ray scattering (WAXS). These CNCSH were used as a reinforcing phase in a NR matrix to prepare nanocomposite films by casting/evaporation at 1, 2.5 and 5 wt% (dry basis) loading levels. The effect of CNCSH on the structure, as well as thermal and mechanical properties of NR, was investigated by means of scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), tensile tests and thermogravimetric analysis (TGA). For the acid hydrolysis treatment, were chose milder conditions compared to those described in Flauzino Neto et al. (2013) in order to avoid as much as possible the hydrolysis of crystalline cellulose domains. The CNCSH was found to have a type I crystal structure, high crystallinity (crystallinity index ≈ 80%), large specific surface area (estimated to be 747 m2.g-1 from geometrical considerations) and high aspect ratio (around 100). This aspect ratio is the largest ever reported in the literature for a plant cellulose source. Futhermore, from microscopic observations it is clearly seen that CNCSH does not consist of partially hydrolyzed microfibril since it displays the classical rod-like morphology of CNC. Thus, soy hull was found to be an interesting source of raw material for the production of CNC, due to the characteristics of the obtained nanocrystals associated with low lignin content and wide availability of this agro-industrial residue. In the meantime, the reuse of this agro-industrial residue goes towards sustainable development and environment-friendly materials. To tailor the dimensions of CNC and take full advantage of this source, special care needs to be paid to the extraction process and its conditions. A milder acid hydrolysis is preferable to improve the extraction yield, preserve the crystallinity of native cellulose and obtain high aspect ratio CNC. As expected, a high reinforcing effect is observed even at low filler contents when using this nanofiller (CNCSH) to prepare nanocomposites with a natural rubber (NR) matrix by casting/evaporation. For instance, by adding only 2.5 wt% CNC, the storage tensile modulus at 25°C of the nanocomposite was about 21 times higher than that of the unfilled NR matrix. This reinforcing effect was higher than the one observed for CNCs extracted from other sources. It may be assigned not only to the high aspect ratio of these CNCs but also to the stiffness of the percolating nanoparticle network formed within the polymer matrix. Moreover, the sedimentation of CNCs during the film processing by casting/evaporation was found to take place and play a crucial role on the mechanical properties. Thus, both the high aspect ratio of the CNC and sedimentation due to the processing technique are involved in the good mechanical results obtained. Indeed, if sedimentation occurs, then a multilayered film results and the CNC content in the lowest layers is higher than the average CNC content. It means that CNC mechanical percolation can occur in the lowest layers for an average CNC content which is lower than the percolation threshold. Hence, the system can be considered as constituted of parallel layers in the direction of the mechanical solicitation (tensile mode), and the CNC-rich layers can support a higher stress leading to a higher modulus value. Moreover, if high aspect ratio CNC is used, then percolation can occur in the lowest layers for lower average CNC contents. An important contribution of this work is to highlight the importance of the sedimentation of CNC during the evaporation step on the mechanical properties of the nanocomposites which is rarely mentioned in the literature.